题解 | #[NOIP1999]回文数#

dic={'0':0,'1':1,'2':2,'3':3,'4':4,'5':5,'6':6,'7':7,'8':8,'9':9,\
    'A':10,'B':11,'C':12,'D':13,'E':14,'F':15}
dic2={0:'0',1:'1',2:'2',3:'3',4:'4',5:'5',6:'6',7:'7',8:'8',9:'9',\
    10:'A',11:'B',12:'C',13:'D',14:'E',15:'F'}

def reverse(x):
    i=len(x)-1
    y=''
    while i>=0:
        y+=x[i]
        i-=1
    return y

def add(n,x):
    y=reverse(x)
    
    z=0
    i=0
    length=len(x)
    while(i<length):
        z*=n
        z+=(dic[x[i]]+dic[y[i]])
        i+=1
    _z=''
    while(z!=0):
        _z+=dic2[z%n]
        z//=n
    return reverse(_z)

def isPalindromic(z):
    z2=reverse(z)
    length=len(z)
    i=0
    while(i<length):
        if z[i]!=z2[i]:
            return False
        i+=1
    return True

n=int(input())
x=input()

z=add(n,x)
idx=1
isImpossible=True
while isPalindromic(z)==False:
    if idx>30:
        isImpossible=False
        break
    z=add(n,z)
    idx+=1
    
if isImpossible==True:
    print('STEP={}'.format(idx))
else:
    print("Impossible!")